Antenna, and communication device using the same

ABSTRACT

An antenna system includes a substrate, a ground on the substrate, a first radiator having a helical shape near a side of the substrate and having a central axis substantially in parallel to a side of the ground, and a high frequency circuit electrically connected to a part of the first radiator. In the antenna system, ground-induced degradation of antenna gain can be reduced, and matching can be performed at an operating frequency through adjustment of a winding of the first radiator. Consequently, the radiation gain of the antenna system can be improved without an antenna matching circuit.

TECHNICAL FIELD

[0001] The present invention relates to a communication device such as asmall mobile terminal or a keyless card terminal, and an antenna systemused in the communication device.

BACKGROUND ART

[0002]FIGS. 12A and 12B show a conventional small antenna used in amobile communication device such as a pager. Loop antenna 100 made ofconductive metal is disposed at a side of display 105 disposed on basesubstrate 104. Antenna 100 has an opening directly perpendicular to thebase substrate. The opening of this antenna is perpendicular to a humanbody when the pager is used in the vicinity of the human body. Since thehuman body can be treated as a reflector, a magnetic current generatedwithin the human body has the same direction as a magnetic dipole formedby loop antenna 100. Accordingly, antenna gain can be increased becausemagnetic fields are added at the front of the human body.

[0003] One end of loop antenna 100 is DC-short-circuited to feeding part102 via first matching capacitor 101 a, while the other end thereof isDC-short-circuited to ground short-circuiting part 103 via thirdmatching capacitor 101 c. Feeding part 102 is coupled to groundshort-circuiting part 103 via second matching capacitor 101 b. Theelement length of the loop antenna is basically set to be equal toone-half wavelength of an operating frequency. For example, pagers inJapan use a 280 MHz band, and one-half of the wavelength of thefrequency is thus about 500 mm. However, an antenna having an elementlength of 500 mm is impractical to build into a small pager. Thus, theloop antenna has its size changed by having the element length shorterthan 500 mm for storage in the pager, and the antenna is matched withmatching capacitors 101 a, 101 b, and 101 c.

[0004] A conventional antenna described above requires the capacitorsfor impedance matching, and power loss in the capacitors causesconsiderable degradation of the radiation gain of the antenna. Inaddition, a ground pattern and a component which are mounted on thesubstrate cause the radiation gain of the antenna to degrade.

[0005]FIG. 13 shows another conventional small antenna used in a mobilecommunication device, such as the pager. This antenna is disclosed inJapanese Patent Publication No.6-93635. Metal plate 1101 is a groundplane, which is an element of a microstrip antenna. Printed board 1105has a circuit for radio communication mounted on metal plate 1101, andconductive plate 1102 is placed over metal plate 1101 via dielectricmember 1104. Conductive plate 1102 has a smaller width than metal plate1101 and faces metal plate 1101. A clearance between metal plate 1101and conductive plate 1102 is filled with dielectric member 1104. Printedboard 1105 is mounted so as not to cover the part where metal plate 1101and conductive plate 1102 face each other. Metal plate 1101 andconductive plate 1102 are mechanically and electrically connected toeach other at their respective ends with connecting plate 1103, so thatmetal plate 1101, conductive plate 1102, and connecting plate 1103cooperatively form a U-shaped microstrip antenna. In order to tune thismicrostrip antenna to a desired frequency, the other end of conductiveplate 1102 is grounded via capacitor 1106, and feeder 1107 is adjustedfor matching.

[0006] The above-described microstrip antenna, due to the inclusion ofthe conductive plate, requires accurate metalworking of its dimensionsfor mass production. Thus, it is difficult to mount the conductive plateto the metal plate. Moreover, single capacitor 1106, since providing themicrostrip antenna with a small range of adjustable impedance, may notachieve the impedance matching due to the effect of a component or metalplaced in the vicinity of the microstrip antenna. Further, the antenna,since being adaptable to only one frequency band, cannot changeoperating frequency according to the application.

DISCLOSURE OF THE INVENTION

[0007] An antenna system includes a substrate, a ground provided on thesubstrate, a first radiator which is provided near a side of thesubstrate, has a helical shape, and has a central axis substantially inparallel to a side of the ground, and a high frequency circuitelectrically coupled with a part of the first radiator.

[0008] In this antenna system, ground-induced degradation of antennagain can be reduced, and matching can be performed at an operatingfrequency through adjustment of a winding of the first radiator.Consequently, the radiation gain of the antenna system can be improvedwithout an antenna matching circuit.

[0009] Another antenna system includes a substrate, a first antennawhich is provided on a first surface of the substrate and surrounds afirst high frequency circuit provided on the first surface of thesubstrate, a second antenna which is provided on the first surface ofthe substrate and adjoins the first antenna, first and second groundswhich are provided on a second surface of the substrate and opposed tothe first high frequency circuit and the second antenna, respectively,and a connecting part which connects the first and second grounds andadjusts respective characteristics of the first and second antennas byhaving its shape adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1A is a top view of a communication device in accordance withexemplary embodiment 1 of the present invention, and FIG. 1B is asection of the communication device.

[0011]FIG. 2 is a top view of an antenna system in accordance withexemplary embodiment 2 of the invention.

[0012]FIG. 3 is a top view of an antenna system in accordance withexemplary embodiment 3 of the invention.

[0013]FIG. 4 is a top perspective view of an antenna system inaccordance with exemplary embodiment 4 of the invention.

[0014]FIGS. 5A to 5C illustrate a relationship between a position of ashort-circuiting through-hole and radiation efficiency of the antennasystem in accordance with embodiment 4.

[0015]FIG. 6 is a bottom view of the antenna system in accordance withembodiment 4.

[0016]FIG. 7 is a bottom view of another antenna system in accordancewith embodiment 4.

[0017]FIG. 8 is a bottom view of still another antenna system inaccordance with embodiment 4.

[0018]FIG. 9 is a top perspective view of an antenna system inaccordance with exemplary embodiment 5 of the invention.

[0019]FIG. 10 is a top perspective view of an antenna in accordance withexemplary embodiment 6 of the invention.

[0020]FIGS. 11A to 11C are top views of respective layers of an antennasystem in accordance with exemplary embodiment 7 of the invention.

[0021]FIG. 12A is a schematic block diagram of a conventional antenna,and FIG. 12B is an outside perspective view of the antenna.

[0022]FIG. 13 is a schematic view of another conventional antenna.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] (Exemplary Embodiment 1)

[0024]FIG. 1 illustrates a card-type communication device in accordancewith exemplary embodiment 1 of the present invention. Base substrate 6has one surface provided with ground 7 and the other surface having highfrequency circuit 5 mounted thereon. Loop antenna 8 of about 100 turnssurrounds ground 7 and high frequency circuit 5. Loop antenna 8transmits and receives a low frequency signal. First radiator 1 havingthrough-holes 2 and a helical conductive pattern printed on the surfaceof base substrate 6 is disposed with its central axis substantially inparallel to a side of ground 7. Thus, radiation gain of an antennasystem can be improved since first radiator 1 forms a magnetic dipoleand a magnetic current induced at the ground of base substrate 6 havethe same direction and are added. This card-type communication devicemay be used, for example, in a pocket of a shirt. Even in this case, themagnetic dipole formed by first radiator 1 and a magnetic currentgenerated within a human body have the same direction, thus increasingthe radiation gain in a direction opposite to the human body. Thus, theantenna system can be used even in the vicinity of the human body.

[0025] By including first radiator 1 and high frequency circuit 5integrated with base substrate 6, the card-type communication device hasincreased strength against bending force. Even in manufacturing, thevariation of performance can be reduced, since the antenna system ispositioned accurately.

[0026] The loop antenna has an element length necessary for matchingaccording to an increase of the number of turns, and therefore, theantenna system does not require a matching capacitor. Positioning acentral axis of the loop antenna in parallel to the side of the groundon the substrate causes a magnetic dipole generated by the loop antennaand the magnetic current induced at the ground to have the samedirection, and consequently, improves the radiation gain.

[0027] Increasing the size of the ground functioning as a part of theantenna system improves radiation efficiency and widens bandwidth of theantenna system.

[0028] The loop antenna may be formed substantially along the peripheryof the ground on at least one of the surfaces of the substrate. This canprevent the bandwidth of the loop antenna from decreasing, and preventsradiation power from being reduced due to the placement of the ground ona back surface of the loop antenna.

[0029] The first radiator may operate for a high frequency signal, whilethe loop antenna may operate for a low frequency signal. The loopantenna, which can have a long element length, is used for communicationat a low frequency, and this provides the antenna system with a highradiation gain.

[0030] (Exemplary Embodiment 2)

[0031]FIG. 2 illustrates a communication device in accordance withexemplary embodiment 2 of the present invention. First radiator 1 ofhelical shape is disposed at a side of base substrate 6 having anelectronic circuit such as high frequency circuit 5 or the like mountedthereon. First radiator 1 has one end connected to high frequencycircuit 5 with feeder 4, and the other end connected to a ground withshort-circuiting line 3. In the vicinity of first radiator 1,meander-shaped second radiator 11 is disposed in an insulated condition.The radiators widen a range of adjustable antenna impedance, whereby theantenna system is usable in two frequency bands. Meander-shaped secondradiator 7, even if having a linear or helical shape, can exhibit thesame characteristic.

[0032] Changing a pitch, element width and element length of themeander-shaped radiator allows the antenna impedance to be adjusted. Byincluding the antenna formed in a conductive pattern on the substrate,the antenna system can be manufactured inexpensively.

[0033] The first radiator may be used for transmission and reception,while the loop antenna may be used only for reception. Communication ata low data rate, that is, in a low frequency takes a lot of time totransmit and receive data. Therefore, the loop antenna may be used onlyfor reception to turn on a built-in circuit of the communication device,and a high frequency signal may be used for actual transmission andreception of data, thus allowing the device to efficiently transmit andreceive the signal.

[0034] (Exemplary Embodiment 3)

[0035]FIG. 3 illustrates a communication device in accordance withexemplary embodiment 3 of the present invention. First radiator 1 hasboth ends connected to a ground by short-circuiting line 3, and anarbitrary point, not being each end, connected to high frequency circuit5 with feeder 4. A position of a connecting point of feeder 4 and firstradiator 1 can adjust an antenna impedance close to 50Ω, and thusprovides the device with a satisfactory radiation characteristi withoutradiation loss caused by an element such as a matching circuit.

[0036] A short-circuiting element for connection to a ground of a metalcase in the vicinity of a feeding part of an antenna enables impedanceto be matched for a loop antenna with a low radiation resistance.

[0037] A communication device including the antenna system ofembodiments 1 to 3, a controller for controlling transmission andreception of a signal, a drive unit for driving the controller, and acase for housing the antenna system, the controller and the drive unitcan perform satisfactory communication even when being used near a humanbody. The communication device may perform only one of the transmissionand reception of the signal.

[0038] (Exemplary Embodiment 4)

[0039]FIG. 4 illustrates an antenna system in accordance with exemplaryembodiment 4 of the present invention. On one surface of base substrate1003, parallel plate antenna 1001 and loop antenna 1002 adjoining eachother and first high frequency circuit 1004 surrounded by loop antenna1002 are mounted. On the other surface of base substrate 1003, firstground 1005 opposed to parallel plate antenna 1001 and second ground1006 opposed to first high frequency circuit 1004 are disposed. Groundconnecting part 1013 connects the first and second grounds and crosses apart of loop antenna 1002. Except a portion corresponding to groundconnecting part 1013, no ground is disposed on a back surface of loopantenna 1002 in order to reduce attenuation of antenna gain. Feedingpart 1014 at an edge of parallel plate antenna 1001 is soldered tofeeding land 1011 to feed parallel plate antenna 1001. Firstthrough-hole 1008 extends from a part of radiating part 1007, except itsedge, to a back surface of the antenna for impedance matching ofparallel plate antenna 1001. An end of the first through-hole that ispositioned at the back surface of the antenna is soldered toshort-circuiting land 1009 at the surface of base substrate 1003. Secondthrough-hole 1010 connects short-circuiting land 1009 and first ground1005. FIGS. 5A to 5C show changes of radiation efficiency of the antennasystem that are calculated by simulation by a moment method against theposition of first through-hole 1008. As the short-circuitingthrough-hole is displaced from the edge (X=0) of the antenna along the Xcoordinate, the radiation efficiency increases accordingly. As thethrough-hole is displaced from the feeding part (Y=0), the radiationefficiency degrades accordingly. This result shows that the antennasystem exhibits satisfactory radiation efficiency when theshort-circuiting through-hole of the parallel plate antenna ispositioned inward from the edge of the antenna in the radiating part ofthe antenna. Impedance matching of parallel plate antenna 1001 can beadjusted by changing the position of the first through-hole. Theimpedance matching can also be adjusted by changing the shape of groundconnecting part 1013 because a high-frequency current passes throughfirst ground 1005, second ground 1006, and ground connecting part 1013during operation of the antenna system. FIGS. 6 and 7 show groundconnecting part 1013 (illustrated by a shaded part) modified in shapefor the impedance matching of parallel plate antenna 1001. FIG. 8 showsan antenna system including first ground 1005 having slits 1014. Themodifications can adjust an impedance characteristic of the parallelplate antenna. The modifications illustrated in FIGS. 6 to 8 can alsoadjust an impedance characteristic of loop antenna 1002 since loopantenna 1002 is magnetically coupled to first ground 1005 and secondground 1006.

[0040] The antenna system of embodiment 4 can flexibly dealing withrespective impedance variations of the first and second antennas causedby the first high frequency circuit or a battery. The first antenna ofthe two antennas, upon being used for standing by for a low frequencysignal, reduces a current consumed in a receiving circuit duringstandby. When used for transmission and reception of data at a highfrequency, The second antenna (the other antenna), upon being used fortransmitting and receiving a high frequency signal, enables the signalto be transmitted and received at high speed.

[0041] The ground may be formed on a portion of the substrate that doesnot have the first radiator and may have the same size as this portion.In a resultant antenna system, the first radiator has a bandwidthprevented from being reduced, and has a radiation power from beingreduced due to a placement of the ground on the back surface of thefirst radiator.

[0042] The antenna system of embodiment 4 is capable of flexibly dealingwith an impedance variation of the first and second antennas that iscaused by the first high frequency circuit or the battery. The firstantenna of the two antennas, upon being used for standing by for a lowfrequency signal, reduces a current consumed in a receiving circuit. Thesecond antenna (the other antenna), upon being used for transmitting andreceiving data at the high frequency, allows the data to be transmittedand received at high speed.

[0043] The first antenna, since being the loop antenna surrounding thehigh frequency circuit, can have a large size. In addition, the antennahas the number of turns adjusted to obtain a desired resonancefrequency.

[0044] The antenna system including the second antenna of the parallelplate antenna can exhibit satisfactory antenna gain even when being usedin close contact with a human body.

[0045] The antenna system of the embodiment, since having the feedingpart not of a metal pin, but of an end face electrode, can bemanufactured and mounted easily. The through-hole is provided inwardfrom the edge of the parallel plate antenna in the radiating part, thusimproving the radiation efficiency.

[0046] According to claim 8 of the invention, an antenna system of claim7 includes a reactance element at an edge of a substrate forming thesecond antenna. The edge is positioned different from the edge providedwith the feeding part. The reactance element has one end connected tothe radiating part of the second antenna and the other end connected toeither the first ground or the second ground. Thus, the second antennacan be tuned to a desired resonance frequency.

[0047] (Exemplary Embodiment 5)

[0048]FIG. 9 illustrates an antenna system in accordance with exemplaryembodiment 5 of the present invention. Reactance loading terminal 1015at an edge of parallel plate antenna 1001 mounted on one surface of basesubstrate 1003 is soldered to land 1016 for the reactance loadingterminal on base substrate 1003. Reactance element 1017 has one endconnected to land 1016 and the other end connected to a ground. This canadjust an impedance characteristic of parallel plate antenna 1001.

[0049] (Exemplary Embodiment 6)

[0050]FIG. 10 illustrates an antenna in accordance with exemplaryembodiment 6 of the present invention. Parallel plate antenna 1001,constructed of a substrate, includes warp-preventing conductor 1019opposed to radiating part 1007. Conductor 1019 is not short-circuited toan end of first through-hole 1008 and prevents the antenna from warpingwhen reflow is conducted for mounting the antenna.

[0051] Antenna 1001, since being formed of the substrate, can be mountedto a board easily in mass production and manufactured inexpensively.

[0052] (Exemplary Embodiment 7)

[0053]FIGS. 11A to 11C illustrate an antenna system in accordance withexemplary embodiment 7 of the present invention. Top substrate layer1020 has parallel plate antenna 1001, loop antenna 1002, and first highfrequency circuit 1004 mounted on its surface. On internal substratelayer 1021, first ground 1005 and second ground 1006 opposed to parallelplate antenna 1001 and the high frequency circuit, respectively, aremounted. On bottom base substrate layer 1022, second high frequencycircuit 1023 and third high frequency circuit 1024 are provided inopposition to the first and second grounds, respectively. Groundconnecting part 1013 is provided between the second and third highfrequency circuits and is connected to first ground 1005 and secondground 1006 through fifth through-hole 1026 and fourth through-hole1025. This configuration allows larger space for the high frequencycircuits, and thus provides a small information terminal.

[0054] A communication device includes any one of the antenna systems ofembodiments 4 to 7, a controller for controlling transmission andreception of a signal, a drive unit for driving the controller, and acase for housing the antenna system. The controller and the drive unitcan perform satisfactory communication even when being used near a humanbody. The communication device may perform only one of the transmissionand reception of the signal.

[0055] Impedance of the antenna system of embodiment 7 can be adjustedby simple work such as trimming of the connecting part or the like.

[0056] In the antenna system of embodiment 7, the position of thethrough-hole is adjusted to adjust a characteristic of the antennasystem. Increasing the number of ways for adjusting the antennaimpedance allows the impedance of each antenna to be matched and reducesreflection loss.

INDUSTRIAL APPLICABILITY

[0057] An antenna system of the present invention that is built in amobile terminal, such as an ID card, a pager, or the like, has animproved radiation gain in free space and has a high radiation gain evenwhen being used near a human body.

[0058] Moreover, the antenna system of the present invention can performsatisfactory impedance matching, thus having less reflection loss andbeing highly efficient. This antenna system is usable at two frequencybands, thus providing high-speed data communication at a high frequencyand low consumption of electric power at a low frequency.

1. An antenna system comprising: a substrate; a ground provided on saidsubstrate; a first radiator provided near a side of said substrate, saidfirst radiator having a helical shape and having a central axissubstantially in parallel to a side of said ground; and a high frequencycircuit electrically coupled with a part of said first radiator.
 2. Theantenna system of claim 1, wherein said first radiator has a first endconnected to said high frequency circuit and a second end connected tosaid ground.
 3. The antenna system of claim 1, wherein said firstradiator has both ends connected to said ground, and is coupled withsaid high frequency circuit between said both ends.
 4. The antennasystem of claim 1, further comprising: a conductive pattern disposed onboth surfaces of said substrate, for forming said first radiator,wherein said high frequency circuit is disposed on said substrate. 5.The antenna system of claim 4, further comprising: a through-hole forconnecting said conductive pattern.
 6. The antenna system of claim 1,wherein said ground has substantially the same size as said substrate.7. The antenna system of claim 1, further comprising: a loop antennadisposed on a surface of said substrate substantially along a peripheryof said substrate.
 8. The antenna system of claim 1, wherein said groundis disposed over a portion of said substrate, said portion excluding aportion of said substrate that has said first radiator.
 9. The antennasystem of claim 8, further comprising: a loop antenna formed on asurface of said substrate substantially along a periphery of saidground.
 10. The antenna system of claim 7 or 9, wherein said firstradiator deals with a high frequency signal, and said loop antenna dealswith a low frequency signal.
 11. The antenna system of claim 10, whereinsaid first radiator can transmit and receive said high frequency signal,and said loop antenna receives said low frequency signal.
 12. Theantenna system of claim 1, further comprising: a second radiatordisposed substantially in parallel to said first radiator, said secondradiator being DC-insulated from said first radiator.
 13. The antennasystem of claim 12, wherein said second radiator has a meandering shape.14. A communication device comprising: said antenna system of claim 1; acontroller for controlling at least one of transmission and reception ofa signal that are performed through said antenna system; a drive unitfor driving said controller; and a case for housing said antenna system,said controller, and said drive unit.
 15. An antenna system comprising:a first substrate; a first antenna on a first surface of said firstsubstrate, said first antenna surrounding a first high frequency circuitprovided on said first surface of said first substrate; a second antennaon said first surface of said first substrate, said second antennaadjoining said first antenna; first and second grounds on a secondsurface of said first substrate, said first and second grounds beingopposed to said first high frequency circuit and said second antenna,respectively; and a connecting part for connecting said first and secondgrounds, said connecting part adjusting respective characteristics ofsaid first and second antennas through being adjusted in shape.
 16. Theantenna system of claim 15, wherein said first antenna is a loopantenna.
 17. The antenna system of claim 15, wherein said first antennadeals with a low frequency signal, and said second antenna deals with ahigh frequency signal.
 18. The antenna system of claim 15, wherein atleast one of said first and second grounds has a slit formed therein.19. The antenna system of claim 16, wherein said second antenna is aplate antenna.
 20. The antenna system of claim 19, further comprising: asecond substrate on said first substrate, for forming said secondantenna.
 21. The antenna system of claim 20, wherein said second antennaincludes: a radiating part on a first surface of said second substrate,said first surface of said second substrate being positioned away fromsaid first substrate; a feeding part provided at an edge of said secondsubstrate; and a through-hole extending from said radiating part to asecond surface of said second substrate, said through-hole being coupledto said second ground.
 22. The antenna system of claim 21, furthercomprising: a reactance element disposed at an edge of said secondsubstrate at a position different from said feeding part, said reactanceelement including a first end coupled to said radiating part of saidsecond antenna and a second end coupled to one of said first and secondgrounds.
 23. The antenna system of claim 20, further comprising: aconductor on said second surface of said second substrate, saidconductor being DC-insulated from said through-hole.
 24. An antennasystem comprising: a multi-layer substrate having a first surface, asecond surface, and a third surface, said first and second surfacesbeing external surfaces, said third surface being an internal surface; afirst high frequency circuit on said first surface of said multi-layersubstrate; a first antenna on said first surface of said multi-layersubstrate, said first antenna surrounding said first high frequencycircuit; a second antenna on said first surface of said multi-layersubstrate, said second antenna adjoining said first antenna; first andsecond grounds on said third surface of said multi-layer substrate, saidfirst and second grounds being opposed to said first high frequencycircuit and said second antenna, respectively; and a connecting part forconnecting said first and second grounds, said connecting part adjustingrespective characteristic of said first and second antennas throughbeing adjusted in shape.
 25. The antenna system of claim 24, furthercomprising: second high frequency circuits on said second surface ofsaid multi-layer, said second high frequency circuits being opposed tosaid first and second grounds, respectively.
 26. The antenna system ofclaim 24, wherein said connecting part is provided on said secondsurface of said multi-layer substrate.
 27. The antenna system of claim26, further comprising: a first through-hole connecting said firstground to said connecting part; and a second through-hole connectingsaid second ground to said connecting part.
 28. The antenna system ofclaim 27, wherein said characteristics of said first and second antennasare adjusted through adjustment of position of at least one of saidfirst and second through-holes.
 29. A communication device comprising:said antenna system of claim 15 or 24; a controller for controlling atleast one of transmission and reception of a signal that are performedthrough said antenna system; a drive unit for driving said controller;and a case for housing said antenna system, said controller, and saiddrive unit.